1. Field of the Invention
The present invention relates to a magnetic resonance (MR) apparatus and, more particularly, to a magnetic resonance apparatus for obtaining the chemical shift information of a specific atomic nucleus in an object to be examined.
2. Description of the Related Art
As conventional methods of obtaining the chemical shift information of a specific nucleus in an object to be examined by utilizing a magnetic resonance method, localized spectroscopy (also called "one-point spectroscopy") disclosed in "BME Vol. 1, No. 3, pp. 169-180 and a chemical shift imaging method (also called "multi-point spectroscopy or phase encoding method") disclosed in "T. F. Budinger, Medical Magnetic Resonance Imaging and Spectroscopy, pp. 81-95, Society of Magnetic Resonance in Medicine, Berkely, Calif., 1986" and the like are known.
Localized spectroscopy is a method of obtaining the chemical shift information of one local area, i.e., one point upon one measurement. In this method, therefore, it takes a long period of time to obtain chemical shift information of a large number of points. For this reason, this method is not suitable for a purpose of obtaining data of large number of points of normal and morbid portions and comparing the obtained data as in the field of clinical diagnoses in medical treatments.
In contrast to this, according to the chemical shift imaging method, chemical information of a large number of points in a wide area can be imaged within a relatively short period of time. However, in the chemical shift imaging method, phase encoding for converting position information in an object to be examined into phase information of a (nuclear) magnetic resonance signal, i.e., an MR signal, is required in the course of acquisition of MR signal and an imaging process. For this reason, if a nuclide having a short T2 (transverse relaxation time) is processed, an MR signal is attenuated while the above phase encoding operation is performed, and an S/N (signal-to-noise ratio) of the MR signal or of chemical shift information obtained upon acquisition of the MR signal is decreased.
As described above, the localized spectroscopy as one of the conventional methods for obtaining chemical shift information is not suitable for a clinical purpose because it requires a long period of time to obtain the chemical shift information of a large number of points. The chemical shift imaging method as another conventional method for obtaining chemical shift information requires an extra time for phase encoding in the course of acquisition of an MR signal and an imaging process. Hence, the chemical shift information of a nuclide having a short T2 cannot be extracted at high S/N ratio.